Traditionally, communication path design selects links within the path based on network requirements for the communication path. Digital transmission systems generally have a set of requirements that include capacity (measured in bits per second), reliability, availability, latency, jitter, bit error rate, and costs. Traditional systems were typically optimized on either capacity or costs, or a combination thereof, while setting threshold requirements for other parameters. In particular there may be a maximum acceptable latency, but cost historically drove much of engineering transmission system design. When engineering a given link, the designer typically would select equipment and routes that provided the lower cost solution.
For business systems, the data rate, or bandwidth offered to a client, is usually the most important driving factor in determining the communication path and technology. Large file transfers typically require high bandwidth, but most requirements had generous thresholds for latency measured in the tens or hundreds of milliseconds or even more. Cost in traditional systems is usually spent to increase the capacity, to improve the reliability and to lower the error rate, rather than to reduce latency So, a customer might want a high speed for the data transfer, but is flexible as to the amount of latency if it reduces cost to the customer. Consequently, while the customer desires an optical link speed, the latency between the points A and B is generally not a key consideration provided a maximal acceptable latency is not exceeded. For example voice systems required the delay to be below that which would be detectable to the human ear (e.g., a few to 100 milliseconds).
Methods to provide a form of graded service typically have focused on the concept of “Quality of Service,” commonly referred to as QoS. In QoS, the service quality is affected by various factors, which can be divided into “human” and “technical” factors. Human factors include: stability of service, availability of service, delays, and other impact to user information. Technical factors include: reliability, scalability, effectiveness, and maintainability. However, for these networks, providing higher levels of QoS (e.g., more bandwidth, higher signal quality, etc.) requires investing more in each user's provisioned service facilities. For example, two users might be provisioned for service between two points. A first user with higher level of service might have a guarantee of a certain high level throughput, the second user a guarantee of a lower level of throughput. Service providers will dedicate more resource, and hence higher expense, to the first user, while dedicating less resource to the second user. Thus, the service provider provides the second user's throughput at less expense, and so charges less for the lower throughput service. But these services do not account for latency in the engineering design of the network at the outset.
Only recently, with computer-executed financial transactions and similar applications, has minimizing latency become of interest, generating a need for ultra-low latency service. Some systems have been designed so that the links provide a relatively shortest terrestrial path between two points A and B to reduce latency, though these systems are restricted to the earth's ground topology when selecting the links. In such systems, termed “ultra-low latency networks” herein, the latency is the signal propagation delay and signal processing delay of both regeneration and repeating. For example, a microwave link or optical fiber link has a propagation delay of the signal through the medium (air or fiber) over the distance traveled, and regeneration delay at microwave towers or optical terminals. Microwave systems have lower propagation delay than traditional fiber systems because the speed of light in optical fiber is only about 70% of the speed of light through air or vacuum. However, because such systems are subject to topology restrictions over the route, an absolute straight line between the two points generally cannot be achieved when the points are separated by a relatively great distance. For example, crossing Pennsylvania, the Appalachians are encountered, and a shortest path might require a tunnel through a mountainside. At the extreme, it would be prohibitively long term and expensive to drill a tunnel between two points to obtain a direct link, and as the distance between the points increases, the tunnel edges closer to the bottom of the earth's mantle. To calculate the total system delay, the processing delay and the propagation delay must be summed and so, from a system standpoint, complex trade-offs are evaluated for a given design.
Such services by ultra-low latency networks have been subject to opposition. As one method of addressing such advantages, agencies have proposed inserting delay at the front end of individual market clients to tune delays experienced by all market users to be substantially equivalent. Thus, all users of the low latency service networks providing such communications would have equivalent grades of service.